Low smoke polypropylene insulation compositions

ABSTRACT

This invention relates to a resin composition comprising polypropylene, a hydrogenated mono alkylarene-conjugated diene block copolymer, oil, and a filler which has been treated with a coupling agent, which can be blended to form a self-extinguishing, low smoke and halogen free insulation composition which exhibits high ultimate elongation and is relatively easy to process.

This application is a divisional application of Ser. No. 802,806 filedNov. 27, 1985. (ABANDONED)

This invention relates to a resin composition comprising polypropylene,a hydrogenated mono alkylarene-conjugated diene block copolymer, oil,and a treated filler which can be blended to form a self-extinguishing,low smoke and halogen free insulation composition which exhibits highultimate elongation and is relatively easy to process.

BACKGROUND OF THE INVENTION

The most common method for reducing the flammability of wire and cableinsulation and jacketing materials is the use of an organic bromine orchlorine compound along with antimony oxide. This system is veryeffective as a flame retardant, but such materials produce a dense blacksmoke when burned, and also produce hydrogen chloride or hydrogenbromide, which are both corrosive and toxic. Because of this, there hasbeen a great deal of interest in flame retarded systems that producelower amounts of smoke and toxic and corrosive gases when they areburned. There appear to be two main approaches that are being followedto meet this goal. The first is to eliminate halogens from the systemand use instead large loadings of alumina trihydrate, another commonfire retardant, or the similar filler magnesium hydroxide. The second isto develop additives that reduce the smoke and acid gas production ofthe halogenated systems. In addition to low smoke low toxicity thesecompositions must also have attractive physical properties in order tobe used for wire and cable applications. These properties includehardness, abrasion resistance, environmental stability, deformationresistance, low temperature flexibility, oil resistance and goodelectrical properties. At present there are no low-smoke, low-toxicity,flame-retardant materials which are readily available although some newmaterials including metal hydrate filled polyethylene are becomingavailable.

Metal hydrates such as alumina trihydrate and magnesium hydroxidecontain water bonded to a crystal structure with the metal atom. Whenheated to a sufficiently high temperature these compounds decompose andrelease water which subsequently varporizes. This process ofdecomposition and vaporization absorbs heat, thus slowing down theinitial heating of the insulation material and consequently slows downthe subsequent burning of the material. After this cooling effect isoverwhelmed however, the presence of the metal hydrates has littleeffect on the subsequent process of burning. Unlike the halogenatedflame retardant composition, metal hydrate compositions withnon-halogenated polyolefins break down quickly into monomer units andburn relatively cleanly without a great deal of smoke production. Inaddition, since metal hydrates only add water to the system, they shouldnot increase the emission of toxic or corrosive gases beyond whatalready would be produced by the system.

Polypropylene, which is readily available at a reasonable cost, hasfound many industrial uses because of its desirable physical properties,such as ease of fabrication by all conventional methods; high meltingpoint of stereoregular, e.g., isotactic, polypropylene and compatibilitywith many other commercial resins, which permits a large number ofblends having specific properties. Brittleness in these compositions canbe reduced either by copolymerizing propylene with ethylene to formblock copolymers or by blending homopolypropylene with rubbers.

Magnesium hydroxide fillers along with alumina trihydrate fillers havebeen used in flame retardant polypropylene compositions. Aluminatrihydrate is generally more effective as a flame retardant than ismagnesium hydroxide due to the greater amount of water incorporated inthat filler, however, magnesium hydroxide has specific advantages, forexample, better processability when incorporated into a polyolefincomposition and a higher decomposition temperature than aluminatrihydrate (330° C. versus 230° C.). This increase decompositiontemperature allows a flame retardant polymer composition containingmagnesium hydroxide to be processed at a higher temperature than acompound with alumina trihydrate. The higher processing temperaturesallow much faster processing due to lower viscosities.

It has been found however that conventional magnesium hydroxide fillerscannot be successfully blended into rubber modified polypropylenecompositions. These compositions when filled to a reasonable loading ofmagnesium hydroxide cannot be processed due to agglomeration of thefiller particles. Accordingly, it would be desirable to provide amagnesium hydroxide filler which would not adversely affect theprocessability by agglomeration.

SUMMARY OF THE INVENTION

According to the present invention there is provided a magnesiumhydroxide filled rubber modified polypropylene composition having goodphysical properties, good processability, good flame retardancy and lowproduction of toxic and corrosive gases when burned, said compositioncomprising

(1) between about 1 and about 40 weight percent of a homopolypropylene,

(2) between 5 and 40 percent by weight of a hydrogenated monoalkylarene-(A)-conjugated diene (B) block copolymer containing at least two Ablocks and at least one B block,

(3) between 1 and about 20 percent by weight of a hydrocarbon extendingoil, and

(4) between about 10 and about 85 percent by weight of a magnesiumhydroxide filler which has been surface treated with a coupling agent.

Detailed Description of the Invention

The compositions of the present invention are prepared by combining therequired components in the correct porportions in conventional blendingequipment such as a rubber mill or mixer, for example, a Banbury mixer.This is usually done above the melting temperature of the polymericmaterials.

Polypropylene

The homopolypropylene preferably should be isotactic and may be, forexample, of the type corresponding to Shell PP-5944 S, PP-5520 and PPDX-5088, available from Shell Chemical Company, Houston, Tex. Mostcommercial isotactic polypropylenes are suitable in the compositions ofthis invention. Syndiotactic homopolymers also can be used. Modifiedpolypropylenes, for example, maleic anhydride functionalizedpolypropylene of the type corresponding to Plexar 2110, available fromNorthern Petrochemical Company, Rolling Meadows, Illinois, may also beused in the compositions of this invention. The functionalizedpolypropylenes are readily prepared according to procedures described inU.S. Pat. Nos. 3,480,580 or 3,481,910, which are hereby incorporated byreference.

Fillers

The magnesium hydroxide fillers useful in the compositions of thepresent invention are surface treated with a coupling agent to preventagglomeration of the particles. When agglomeration occurs the effectiveparticle size of the filler is increased dramatically and therefore theprocessability and the properties of the end product are degraded.Surfactants which are useful in the invention may include fatty acidsalts, for example, oleates and stearates, also maleates, silanes,zirco-aluminates, titanates, etc. It has also been found that magnesiumhydroxide fillers with a high aspect ratio crystallate shape and largersize are also less likely to agglomerate than those with a lower aspectratio. Aspect ratios for the crystallites should be greater than 4 andmean secondary particle (agglomerate) size should be less than threemicrons.

Block Copolymers

The hydrogenated monoalkyl arene-conjugated diene block copolymersuseful in the present invention are well known in the art. This blockcopolymer, as defined in U.S. Pat. No. 4,110,303, among other patents,has at least two monoalkenyl arene polymer end blocks A and at least onepolymer mid block B selected from the group consisting of substantiallycompletely hydrogenated conjugated diene polymer blocks,ethylene-propylene polymer blocks and ethylene-butene polymer blocks.The block copolymers employed in the present invention may have avariety of geometrical structures, since the invention does not dependon any specific geometrical structure, but rather upon the chemicalconstitution of each of the polymer blocks. Thus, the structures may belinear, radial or branched so long as each copolymer has at least twopolymer end blocks A and at least one polymer mid block B as definedabove. Methods for the preparation of such polymers are known in theart. Particular reference will be made to the use of lithium basedcatalysts and especially lithium alkyls for the preparation of theprecursor polymers (polymers before hydrogenation). U.S. Pat. No.3,595,942 not only describes some of the polymers of the presentinvention but also describes suitable methods for their hydrogenation.The structure of the polymers is determined by their method ofpolymerization. For example, linear polymers result by sequentialintroduction of the desired monomers into the reaction vessel when usingsuch initiators as lithium-alkyls or dilithiostilbene and the like, orby coupling a two segment block copolymer with a difunctional couplingagent. Branched structures, on the other hand, may be obtained by theuse of suitable coupling agents having a functionality with respect tothe precursor polymers of three or more. Coupling may be effected withmultifunctional coupling agents such as dihaloalkanes or alkenes anddivinyl benzene as well as certain polar compounds such as siliconhalides, siloxanes or esters of monohydric alcohols with carboxylicacids. The presence of any coupling residues in the polymer may beignored for an adequate description of the polymers forming a part ofthe compositions of this invention. Likewise, in the generic sense, thespecific structures also may be ignored. The invention appliesespecially to the use of selectively hydrogenated polymers having theconfiguration before hydrogenation of the following typical species:

polystyrene-polybutadiene-polystyrene (SBS)

polystyrene-polyisoprene-polystyrene (SIS)

poly(alpha-methylstyrene)-polybutadiene-poly(alpha-methylstyrene) and

poly(alpha-methylstyrene)-polyisoprene-poly(alpha-methylstyrene).

It will be understood that both blocks A and B may be either homopolymeror random copolymer blocks as long as each block predominates in atleast one class of the monomers characterizing the blocks and as long asthe A blocks individually predominate in monoalkenyl arenes and the Bblocks individually predominate in dienes. The term "monoalkenyl arene"will be taken to include especially styrene and its analogs and homologsincluding alpha-methylstyrene and ring-substituted styrenes,particularly ring-methylated styrenes. The preferred monoalkenyl arenesare styrene and alpha-methylstyrene, and styrene is particularlypreferred. The blocks B may comprise homopolymers of butadiene orisoprene and copolymers of one of these two dienes with a monoalkenylarene as long as the blocks B predominate in conjugated diene units.When the monomer employed is butadiene, it is preferred that betweenabout 35 and about 55 mol percent of the condensed butadiene units inthe butadiene polymer block have 1,2 configuration. Thus, when such ablock is hydrogenated, the resulting product is, or resembles a regularcopolymer block of ethylene and butene-1 (EB). If the conjugated dieneemployed is isoprene, the resulting hydrogenated produce is or resemblesa regular copolymer block of ethylene and propylene (EP).Ethylene-butene or ethylene-propylene blocks prepared via directpolymerization and not by hydrogenation of conjugated diene polymerblocks are also contemplated by the present invention.

Hydrogenation of the precursor block copolymers, if required, ispreferably effected by use of a catalyst comprising the reactionproducts of an aluminum alkyl compound with nickel or cobaltcarboxylates or alkoxides under such conditions as to substantiallycompletely hydrogenate at least 80% of the aliphatic double bonds whilehydrogenating no more than about 25% of the alkenyl arene aromaticdouble bonds. Preferred block copolymers are those where at least 99% ofthe aliphatic double bonds are hydrogenated while less than 5% of thearomatic double bonds are hydrogenated.

The average molecular weights of the individual blocks may vary withincertain limits. In most instances, the monoalkenyl arene blocks willhave number average molecular weights in the order of 5,000-125,000,preferably 7,000-60,000 while the conjugated diene blocks either beforeor after hydrogenation will have average molecular weights in the orderof 10,000-300,000, preferably 30,000-150,000. The total averagemolecular weight of the block copolymer is typically in the order of25,000 to about 250,000, preferably from about 35,000 to about 200,000.These molecular weights are most accurately determined by tritiumcounting methods or osmotic pressure measurements.

The proportion of the monoalkenyl arene blocks should be between about 8and 55% by weight of the block copolymer, preferably between about 10and 35% by weight.

Additional Components

In addition, The present composition may contain other components suchas plasticizers, e.g., saturated hydrocarbon or mineral oils,hydrogenated or saturated hydrocarbon resins along with additives suchas stabilizers and oxidation inhibitors. Aliphatic oils and resins arepreferred to aromatic oils and resins since aromatics tend to cyclacizeresulting in color bodies. Preferred oils are primarily aliphatic,saturated mineral oils. Preferred resins are saturated or hydrogenatedhydrocarbon resins, such as hydrogenated polymers of dienes and olefins.These additional components must be compatible with the block copolymercomponent. The selection of the other components depends upon a numberof factors--e.g., the method for coating a wire.

As stated above, the compositions may be modified with supplementarymaterials such as stabilizers and oxidation inhibitors. Stabilizers andoxidation inhibitors are typically added to the compositions in order toprotect the polymers against degradation during preparation and use ofthe composition. Combinations of stabilizers are often more effective,due to the different mechanisms of degradation to which various polymersare subject. Certain hindered phenols, organo-metallic compounds,aromatic amines and sulfur compounds are useful for this purpose.Especially effective types of these material include the following:

1. Benzothiazoles, such as 2-(dialkyl-hydroxybenzyl-thio)benzothiazoles.

2. Esters of hydroxybenzyl alcohols, such as benzoates, phthalates,stearates, adipates or acrylates of 3,5-dialkyl-1-hydroxy-benzylalcohols.

3. Stannous phenyl catecholates.

4. Zinc dialkyl dithiocarbamates.

5. Alkyl phenols, e.g., 2,6-di-tert-butyl-4-methyl phenol.

6. Dilaurylthio-dipropionate (DLTDP). Examples of commercially availableantioxidants are "Ionox 220" 4,4-methylene-bis(2,6-di-t-butyl-phenol)and "Ionox 330"3,4,6-tris(3,5-di-t-butyl-p-hydroxybenzyl)-1,3,5-trimethylbenzene,"Dalpac 4C" 2,6-di-(t-butyl)-p-cresol, "Naugawhite" alkylated bisphenol,"Butyl Zimate" zinc dibutyl dithiocarbamate, and "Agerite Geltrol"alkylated-arylated bisphenolic phosphite. From about 0.01 percent toabout 5.0 percent by weight of one or more antioxidants is generallyadded to the composition.

                  TABLE I                                                         ______________________________________                                                  Typical Preferred  Most Preferred                                   ______________________________________                                        Block Copolymer                                                                           5-40      10-30      15-20                                        Plasticizer (oil)                                                                         1-20      2-15       4-8                                          Polypropylene                                                                             1-40      2-20       4-8                                          Filler      10-85     40-75      63-75                                        ______________________________________                                    

The particular amounts of each component may vary somewhat in theresultant composition depending on the components employed and theirrelative amounts.

Examples

The following examples are given to illustrate the invention and are notto be construed as limiting.

The components used where as follows:

Block Copolymer 1 is a S-EB-S with GPC block molecular weights of about29,000-125,000-29,000.

Block Copolymer 2 is a S-EB-S with GPC block molecular weights of about10,000-50,000-10,000.

Block Copolymer 3 is a S-EB-S with GPC block molecular weights of7,000-35,000-7,000.

The oil was Penreco 4434 oil available from Penreco Company. Thepolypropylene was homopolypropylene PP 5520 from Shell Chemical Company.The modified polypropylene was a maleic anhydride functionalizedpolypropylene, Plexar 2110 from Northern Petrochemical Company inRolling Meadows, Ill. The ATH was alumina trihydrate, 1.0 micronprecipitated Hydral 710B from Alcoa. The Mg(OH)₂ was from Ventrondivision of Morton Thiocol Inc. with a secondary (aggregate) particlesize of about 4 microns. Surface treated Mg(OH)₂ was Kisuma 5B fromKyowa Chemical Industry Ltd. which is oleate treated and has an averagesecondary (aggregate) particle size of about 0.8 microns.

Antioxidants

Irganox 1010; tetra-bismethylene 3-(3,5-ditertbutyl-4hydroxy-phenyl)-propionate methane from Ciba-Geigy.

Irganox MD-1024; stabilizers from Ciba-Geigy.

DLTDP; Plastanox DLTDP, American Cyanamid.

Compositions are in percent by weight.

Examples were extruded insulation coating on 18AWG solid conductor 30mils samples. All insulation coatings were conducted at 190 deg. C melttemperature.

Control examples IC 1132 and IC 1100 show properties for control blendswith conventional Mg(OH)₂ and ATH respectively. These were either notable to be coated or were difficult to process as indicated by the lowscrew speed and high power input. The examples according to theinvention contained the treated Mg(OH)₂ and showed good comparablephysical properties plus good processability. LR 8506 containedhomopolypropylene while the remaining examples according to theinvention contained maleic anhydride functionalized polypropylene.

    TABLE II      Block Copolymer IC 1132 IC 1100 LR 8506 IC 1104 IC 1157 IC 1158 IC 1162 I     C 1163 IC 1187 IC 1188 IC 1189 IC 1192 IC 1193       Block Copolymer 1 14.70% 15.70% 16.00% 14.70% 7.35% 18.37% 18.05%     21.40% 16.32% 17.67% 14.97% -- -- Block Copolymer 2 -- -- -- -- -- -- --     -- -- -- -- -- 16.32% Block Copolymer 3 -- -- -- -- -- -- -- -- -- -- --     -- -- Oil 7.35% 7.85% 8.00% 7.35% 7.35% 3.68% 4.00% 4.00% 5.68% 5.68%     5.68% 7.35% 7.35% Polypropylene -- -- 5.00% -- -- -- -- -- -- -- -- --     -- Modified Polypropylene 7.35% 7.85% -- 7.35% 14.70% 7.35% 7.35% 4.00%     7.35% 6.00% 8.70% 7.35% 7.35% ATH -- 68.00% -- -- --  -- -- -- -- -- --     -- -- Mg(OH).sub.2 70.00% -- -- -- -- -- -- -- -- -- -- -- -- Surface     Treated Mg(OH).sub.2 -- -- 70.40% 70.00% 70.00% 70.00% 70.00% 70.00%     70.00% 70.00% 70.00% 70.00% 70.00% Irganox 1010 0.10% 0.10% 0.25% 0.10%     0.25% 0.25% 0.25% 0.25% 0.25% 0.25% 0.25% 0.25% 0.25% Irganox 1024 0.10%     0.10% 0.10% 0.10% 0.10% 0.10% 0.10% 0.10% 0.15% 0.15% 0.15% 0.15% 0.15%     DLTDP 0.40% 0.40% 0.25% 0.40% 0.25% 0.25% 0.25% 0.25% 0.25% 0.25% 0.25%     0.25% 0.25% Stress Break (psi) * 1130 400 960 970 1370 1350 1210 1260     980 1230 1090 950 Elongation at Break (%) * 300 370 250 0 350 330 320     300 330 350 600 600 Line speed (FPM) * -- 250 -- 50 45 50 50 50 50 50 50     50 Screw speed (RPM) * 20 150 30 29 28 36 34 30 30 30 30 30 Power Input     (AMP) * 27 10 17 13 23 24 23 16 19 20.5 17 14 Head Pressure (psi) * 7900     1340 4000 3100 5200 5500 5000 4000 4700 4800 4600 3500 Limiting Oxygen     Index % * 30.0 0.31 29.5 28.5 30.0 -- -- -- 34.0 31.0 -- --     *Could not be coated.

What is claimed is:
 1. An electrically conductive wire extrusion coatedwith a flame retardant insulation composition comprising:(a) 15-20percent by weight of a hydrogenated styrene-butadiene-styrene blockcopolymer; (b) 4-8 percent by weight of a plasticizer; (c) 4-8 percentby weight of polypropylene; (d) 63-75 percent by weight of a hydratedmagnesium hydroxide which has been surface treated with a couplingagent, wherein the magnesium hydroxide has a mean particle size of about0.6 to about 1.2 microns and a crystallite aspect ratio greater than 4.2. The wire of claim 1 wherein the polypropylene has a functional groupgrafted to it.
 3. The wire of claim 3 wherein the functional group ismaleic anhydride.
 4. The wire of claim 3 wherein the coupling agent is afatty acid metal salt.
 5. The wire of claim 1 wherein the coupling agentis an oleate.
 6. The wire of claim 1 wherein the coupling agent is astearate.
 7. The wire of claim 1 wherein the coupling agent is amaleate.
 8. The wire of claim 1 wherein the coupling agent is a silane.9. The wire of claim 1 wherein the coupling agent is a titanate.
 10. Thewire of claim 1 wherein the coupling agent is a zirco-aluminate.
 11. Thewire claim 1 wherein the plasticizer is a mineral oil.